This invention relates to communication cables in general and more particularly to the mechanical design of a symmetrical communication cable such as is used, for instance, for wiring purposes in telephone exchange installations, and the design of which takes into consideration the possibility of terminating the cable ends, i.e., assembling connectors automatically, and also to a method and apparatus of manufacturing such a cable.
In the manufacture of symmetrical communication cables, the individual twisting elements such as pairs, triplets or quads are twisted in layers or groups to form the cable core. If communication cables are built up in groups, this has advantages with respect to the mounting of fittings and with respect to wiring. For instance, five spiral quads or five to ten conductor pairs can be twisted to form a base group and subsequently, several such base groups twisted to form a main group. Such a main group or several such main groups form the cable core (German Petty Patent No. 66 07 289).
In one known symmetrical communication cable of group design, several such conductor pairs are combined in pair groups which are twisted together to form the cable core which is surrounded by a cable sheath. The pairs of each pair group form a kind of flat cable, inasmuch as the pairs are connected to each other transversely to the lengthwise direction of the conductors by means of flexible holding elements arranged at regular intervals. The flexible holding elements can each consist of two plastic strips which are welded or cemented together laterally to the pairs (German Offenlegungsschrift No. 17 65 463). Through such a design of the communication cable, which is provided particularly as a wiring cable for telephone exchange installations, the cost for marking the individual conductors and pairs as well as for the wiring of the cable ends can be reduced. In another cable of this type, the conductors of each conductor group (base group) are arranged side by side on a tape-like carrier and the carrier with the conductors is formed into a tabular structure which represents the base group (German Offenlagungsschrift No. 20 21 875). In addition, a wiring cable consisting of a so-called ribbon cable is known in which the ribbon cable is alternatingly folded right and left for improving its flexibility and is enclosed by a sheath (U.S. Pat. No. 2,004,612). Ribbon cables, in which a number of individual insulated conductors is fastened via their insulation to a common carrier member, can be fabricated, incidentally, by first arranging the conductors about a fixed arbor, then spray-molding the conductors on their sides facing away from the arbor with a common plastic sheath and by finally cutting open the plastic sheath between two conductors parallel to the latter, after the arbor has been removed, and bending it open to form the carrier member (German Auslegeschrift No. 15 15 813).